Zoned resistor for electric furnaces



May 22, 1928.

F. T. COPE ZONED RESISTOR FORELECTRIC FURNACES Filed Feb. 24, 1925attonlugd Patented May 22, 1928.

UNITED STATES rnanx '1'. corn, or samm, onro, assrenon. To run nnnc'rarcsummon coiurariir,

1,670,846 PATENT OFFICE.

OI SALEM, OHIO, A. CORPORATION OF OHIO (INCORPORATED 1928).

' Application filed February 24, 1925. Serial No. 11,265.

This invention relates to electric furnaces of the resistor type andmore particularly to resistors of the grid type. The invention isespecially applicable to furnaces of the continuous type and may also becarried out in other types of furnaces where it is necessary ordesirable to compensate for an unequal cooling or overheating efiect incertain portions of the furnace.

In continuous electric furnaces, in which the material is moved throughthe furnace in one direction,-it is customary to provide resistor gridsupon thewalls of the furnace, extending from end to end of the heatingchamber, a substantially uniform amount of energy being supplied to allparts of the resistor.

also cools the discharge end of the eatin chamb'er, making it impossibleto hold the "material at temperature until discharged from the furnace.This is objectionable ,in

With this form of furnace, the temperature within the heating chamber,at. the charging end, is kept down considerably below therulingstemperature of the'furnace, due to rapid a cold material, ma 'ngit practically impossible to quickly bring the material to the desiredtemperature, since a high tempe'ra-.

ture differential cannot exist between the resistor and the coldin-comin stock without overheatin the balance of t e furnace.

The cooling effect of the dischar e door the heat treating of steel andthe like as it is usually desirable to bring the material to a specifiedtem erature in a reasonably short timefand hol the temperature untildischarged from the furnace.

The objects of the present invention are to zone or segregate theresistors to overcome the cooling effect of the material and furnacedoors in order that the material may be quickl brought to, the desiredtemperature and eldat such temperature until discharged from thefurnace.

The above and other. objects may be attained by providing a plurality ofresistors throughout the furnace and directing diiferent amounts ofenergy to different, resistors, thus substantially zoning thetemperature of the heating chamber.

An embodiment of the invention is illustrated in the accompanyingdrawing, in

or tion of heat by in-corning' the furnace zoned by means of a pluralityof resistor grids receiving different amounts ofenergy;

i 1g. 2, a diagram showing the temperature gradieint of a furnace suchas shown in Fig.

Fig. 3, a similar view of the usual temperature gradient of a furnacewhere the same amount of energy is directed throughout the length of theresistor. 1

Similar numerals refer to similar parts throughout the drawing.

For the purpose of illustration, :1 continuous furnace which may be saidto havevan electrical capacity of 100 kw., is shown, the heating chamberbeing indicated at 1 and adapted to be heated by three sets of resistorgrids as shown at 2, 3 and 4, substanchamber into three zones extendingfromthe charging'end to the discharge end thereof.

The resistors 2, which extend from the charging end to a .point near thecenter of the heating chamber, are connected to the Wires 5 throughwhichthey are adapted to receive kw. of electrical energy.

Theresistors 3, in thecentral zone of the furnace, are connected to thewires' 6, through which they are adapted to receive g 30 kw. The shortresistors 4 at the discharge end of the furnace may receive 10 kw.

through the wires 7.

. With this arrangement of resistor grids the furnace is effectuallyzoned-to produce a temperature gradient asshown in Fig. 2.

Assuming the cold material entering the charging end of the furnace tobe substantially 6U F., the temperature curve will rise rapidly asshown, as the material passes through the firstzone, the resistors 2running at 60 kw., bringing the material to the desired-temperature,indicated at 1550", in a comparatively short time, due --to the largeramount of ener y being liberated in the first zone; whereas i a uniformamountof energy is deliveredthroughout the entire furnace,

loo

the heating time of the material will be considerably extended 'due tothe lower amount of heat liberated at the charging end of the furnace.

The resistors 3, inthe central zone, running at 30 kw., will liberatesuflicient energy' within the central zone of the furnace to hold thetemperature at 1550, and the cooling effect of the discharge doorisovercome I by providing the short resistors 4; which rece1ve 10 kw.,liberating a. greater amount of energy in a given space, due to the factthat they arev operated at. a higher current density, than thecentralresistors and maintaining the temperature at l550 until it reaches thedischarge door of the furnace.

ln higrii is shown a typical temperature gradient of a furnace in whichthe resistor extends from one end of the furnace to the other andreceives a uniform amount of ento control two or more zones by the samecontrol outfit, it being 0t course understood that such an arirangementwould not inter ere with delivering difierent amounts of energy to thezones so controlled.

A control outfit includes a contact pyrometer 8, of standard type andprovided with a needle 9 arranged to swing into contact with each or theplates 10 when depressed by the depressor bar 11, which may be clock ormotor operated, depending uponthe type of pyrometer used. v-Eachpyrometer .15 controlled by a thermo-couple 12 extending into thecorresponding zone of the-furnace and connected to the pyrometer as bywires 13.

By contacting with either of the contact points 10 and 10, the needlecompletes a circuit through the wires 14 and 15, from the line wires-16, to one or the other of the solenoids 17 operating the relay switch18, which controls the solenoid operated switch 19, through which thecircuit from the wires 16 to the resistors,.is completed.

in the central circuit as shown, when the temperatureot" thecorresponding zone is below the predetermined setting of the controlpyrometer, contact will be established from the depressor bar 11 tocontact point 10, closing the relay switch 18 which, in turn,closes themain line," magnet operated switch 19,

thus connecting the resistor within that zone with the line 16.

The temperature within the zone controlled will immediately start torise and will continue to rise until the needle 9swings out of contactwith point 10 and across the intervening space between the contacts 10 Ii and 10*, which distance, for the purpose of illustration, may beequivalent to 10 or 15 F.

. neadeee As soon, however, as the needle contacts the relay switch-18,'in turn opening the main line switch 19 and cutting the current on ofthe particular zone. 'lhe needle 9 will again start to recede to againcontact with point 10, which action it is seen will maintain thetemperature of the controlled zone 1Within a predetermined limit of 10or 15 For the purpose of. varying density of the resistors, a manuallyoperated multiple point switch is provided and comprises the switchblade'2l, to which one of the wires .16 is connected, and the contactpoints 22, arranged to be selectively engaged by said blade and tappedat spaced intervals to the secondary coil 23', which'is connected to theother wire 16. 'lhe primary coil 24 of the transformer is connected tothe line wires25. v.

This multiple point switch is arranged to be manually operated toindependently control the current density of each resistor, while theduration of time during which current is delivered to each resistor isautomatically controlled by the thermally controlled outfit.

it will, of course, be seen that each of the pyrometers may be set tomaintain the corresponding zone of the furnace at the desiredtemperature for that particular zone in order to accomplish the resultsas above described.-

Although the invention is illustrated and described as applied to acontinuous furnace in which the material is constantly moved through thefurnace in one direction, it should be understood that the invention isalso applicable to other forms of furnaces where differentialtemperatures are desired.

It is known that furnaces have been constructed in which the resistorshave been placed closer together or hung in parallel rows at certainpoints and it should be understood that no claim is made to such a"construction as a uniform amount of energy is released throughout theentire length of the resistor, and the current density is not increasedat these points; while in the presthe current ent case difierentialamounts of ener 'y are released from dillerent portions of t e resistormeans, the current density being increased at the points where greateramounts of. energy are released.

I claim: 1. An electric furnace including a plurality of zones, aresistor located ineach zone of the furnace, means for liberating adifferent amount of heat from each resistor,

and means controlled by the temperature in each zone for regulating theamount of energy deliveredto the corresponding resistor. 2. An electricfurnace including resistors sistors.

name

'each resistor having a different capacity for liberating energy, andmeans for varying the current density in certain of said resistors.

3. An electric furnace having segregated zones, electric resistorslocated within said zones, each resistor having a different capacity forliberating energy so that a predetermined temperature gradient is produced in the furnace, and controlled means for operating certain of theresistors at a higher current densi 4. An electric furnace including apluralit of zones, a resistor located in each zone of the furnace, eachresistor having a different capacity for liberating energy, and meanscontrolled by the temperatures. in the differentzones for delivermgdifierent amounts of energy to the several resistors.

5. An electric furnace including a plurality of zones, a resistor,located in each controlled.

zone in thefurnace, manualliy e means for varying the current nsity 'inthe ty than the other re-' difi'erent resistors and p rometer controlledmeans for controlling current in each resistor.

t e duration of the 6; A continuous electric furnace having segregatedresistors, each resistor having a different capacity for liberatingenergy so as to zone t e furnace to produce a predetermined temperaturegradient, and rometer controlled means for controlling the length oftime during which current is delivered to each resistor.

7.A continuous electric furnace having rega-ted resistors, each resistorhaving a fierent capacity for liberating energy so as to zone thefurnace to produce a predetermined temperature gradient, manuallycontrolled means for varying the current density in the difierentresistorsand pyrometer controlled means 7 for controllin the length oftime during which current is delivered to each resistor.

, In testimony that I claim the above, I

have-hereunto subscribed my name.

FRANK T. em.

